The present invention relates to a reconfigurable fiber-optic sensor.
Fiber-optic temperature or stress sensors have been the subject of numerous studies throughout the world. The field of intrinsic temperature or stress sensors has expanded particularly by virtue of the use of an optical fiber as the sensor (use of high-birefringence or polarization-maintaining optical fibers).
Production of optical sensors distributed along a birefringent fiber has made it possible to use N elementary sensors corresponding to N segments of sensor fiber. These various segments are defined by using coupling points serving as markers (delimiting these segments).
The production of coupling points on optical fibers has been studied for a long time, and today various production techniques are used, among which are:
splicing of two sections of the same fiber, that is to say cutting the fiber and bonding the two portions after having rotated one of the fiber portions through an arbitrary angle. The main drawbacks of this method are the introduction of losses due to the reflections off the faces of the fibers and the control of the alignment and rotation of the fiber cores (diameter of the order of 5 .mu.m); PA1 melting of the fiber using localized heating. A section of the birefringent fiber of chosen length is held at its ends and the fiber is rotated at one end, the other remaining fixed. A torsional stress is thus created. Using localized heating of the fiber, a polarization coupling point is thus produced. The drawbacks of this method are the use of a locally stripped fiber, a high-voltage generator and an electric arc in order to create the coupling point or points, and the irreversibility of the method of creating the coupling points; PA1 the production of index gratings in the fiber using a masking method or using a holographic method. The production of coupling points using this method is nowadays mainly studied by the BERTIN Company and many studies have concerned the production of index gratings in the fibers for sensor applications. The drawback of this method resides in its complexity of implementation, the need to use an additional high-power laser to produce the index gratings, and the need to employ a process for masking the fiber.
From the German Document DE-A-4,011,440, a fiber-optic temperature sensor is known, to which an element, which may be made of shape-memory alloy, applies a longitudinal stress deforming this fiber into a "U". This sensor enables only the measurement of a single temperature to be made and does not enable the location, where the stress induced by the measured temperature change has occurred, to be located precisely. In addition, the deformation produced by the SMA element is not reversible.